For the past year, the engineering Division has been engaged in the analysis, design, and construction of many basic elements of a novel commercial communication satellite system. The communication link consists of a very light active repeater in a synchronous equatorial orbit used in conjunction with two or more ground terminals as an intercontinental relay of television, telephone, and teletype messages.
While the use of a stationary Earth satellite as a radio relay was described as early as 1945, and current trade publications bristle with air-brush drawings of similar systems, the Hughes concept is felt to be unique in the combination of techniques and integration of functions which have resulted in a payload small enough to be boosted into orbit by the NASA Scout. The use of this low-cost solid propellant booster, currently under development, accounts for the commercial attractiveness of this system.
The payload repeater consists of a transistorized UHF receiver and a 2.5 watt, S-band traveling wave tube transmitter. Electrical power is supplied by solar cells which cover its cylindrical surface. The receiver-transmitter, in addition to serving as a communication relay, is used as a guidance signal repeater during launch guidance. The receiver is also used as a command receiver, and the transmitter as a telemetering transmitter.
Because the stationary orbit has a range of about 22,752 nautical miles, a directional antenna must be employed to keep the required payload transmitter power low. Where other systems have resorted to attitude stabilization to properly aim the directional antennas, the Hughes system achieves the desired directivity in a spin stabilized configuration. The use of spin stabilization affords a substantial simplification of the vernier orbital correction system, which requires only two pulsed gas jets for complete velocity and spin orientation control.
A launch guidance system is used to measure the booster velocity, so that it can be cut off at the desired value. Fortunately, the guidance precision required to reduce the initial errors to within the range of the vernier control system turns out to be only moderate, an order of magnitude less critical than a ballistic missile guidance system. A medium power UHF transmitter, an angle tracking S-band receiver, and a second fixed receiver displaced 10,000 feet from the first to form an interferometer are used to determine the range, range rate, elevation angle, and elevation angle rate with the required precision.
Five hours and 20 minutes after launch, a “kick in the apogee” is used to achieve a nominally synchronous orbit. At this stage, the synchronous apogee controller is employed to command the jets in the payload, first to orient the spin axis, then to null out the velocity errors. This clever little machine, which actually goes “pucketa- pucketa” when it’s running, is “tuned in” to the payload spin speed and by means of mechanical phase shifters generates the appropriate commands.
The ground communication terminals will contain large fixed antenna, a high power UHF transmitter, and a low S-band receiver. The latter will contain a liquid-nitrogen cooled parametric amplifier.
A payload based on the above concept, but designed to be launched by the Thor-Delta, has been constructed. The Thor-Delta configuration was intended to make possible an experimental launch at an early date before a fully developed Scout could be made available. NASA is currently considering a proposal for an experiment which could lead to a commercial communication system. In addition, Hughes is investigating means of exploiting the commercial possibilities of the system.
The idea of a lightweight spinning synchronous repeater using spin phased impulses for orbital corrections was conceived by Dr. Harold A. Rosen, now manager of the project. A preliminary design based on the concept was worked up last fall by him and two senior staff scientists, Tom Hudspeth, who was responsible for the detailed electronic design and Don Williams, who contributed the orientation method and a detailed dynamic analysis of the entire system.
After a rigorous review, Hughes management became sufficiently convinced of its value to support the development of the payload and guidance system while efforts were being made to secure support elsewhere for other essential elements of the system.
At its peak, more than 50 engineers and technicians were employed on the project, and the program has been outstanding.
In the Radar and Missile Electronics Laboratory, which has responsibility for the payload electronics and guidance system development, Eddie Phillips supervises the command circuit design, Meredith Eick, the guidance system development, Tom Hudspeth, the development of the repeater electronics and Jim Morse and Clem Quella designed the electronics chassis. Don Williams designed the solar sensors and the synchronous control system.
In the Aero/Space Vehicle Laboratory, which has responsibility for the mechanical and thermal design of the payload. Ed Marriott is the project manager. Ralph Colbert supervises the structural design and integration of the various units, Howard Prochaska the electrical power system composed of the solar cells and space batteries and Bob Telle the control valves and high pressure nitrogen tanks. The detailed trajectory calculations are made by Jim Belardi and the temperature environment and passive temperature control system by Conrad Stensguard.
The space environment and plans for environmental tests are being defined by Ed Felkel and Dick Baker of the Product Assurance and Space Installation Department, Air Defense Laboratories.
A compact, efficient traveling wave tube is being developed specifically for the project by a group in the Microwave Tube Division under Dr. Dave Baln and Dr. John Mendel. Richard Notvest, Bruce Highstreit, Ron Forbes are among those contributing to its development.
The low noise amplifier for the ground terminals is being developed in the Research Laboratories by Rolf Weglein working under Dr. Mal Currie.